Jan H. Sällström, Johan Sandström, Sven E. Sällberg
Papers # 2016 Berlin
Flange joints connecting plastic pipes to valves are studied. The pipes have a reduced flange adaptor or a HP-flange adaptor. In the full scale experiments all flanges have a bolt circle diameter Ø725 mm. Four types of gaskets are used: an O-ring, a standard and a profiled gasket of EPDM with a steel core without and with an O-ring part, respectively, and also a planar gasket. In parallel, finite element analyses have been used for simulating the bolt tightening and relaxation of the flange joints investigated.
Water tightness of flange joints at valves has been investigated. Two flange adaptors of polyethylene have been used in the experimental and numerical studies. Four different gaskets have been studied: an integrated O-ring along with a reduced flange, a standard and a profiled rubber gasket with the steel core without and with the O-ring part, respecttively, and also a planar gasket. In the experiments, threads and other slip surfaces have been lubricated to achieve an even distribution of bolt forces and less friction losses.
Large variations in the bolt forces are measured. A simulation shows that despite the large variations, the sealing pressure in the circumferential direction is constant when a rubber gasket with the steel core is used.
Experiments have shown that for the profiled rubber gasket, it took less than 60 % of the recommended torque to achieve tightness. This applies also to the reduced flange with the integrated O-ring.
In all experiments the joints remained tight during the test period of more than a week. The simulations show that the tightness is preserved for 100 years for all the studied joints with the profiled rubber gasket. HP-flange remains tight for 100 years with all types of studied gaskets.
To obtain tight joints this study supports the use of profiled rubber gaskets with the steel core and the O-ring part or, alternatively, reduced flanges with integrated O-rings.
Advantages of using primarily the profiled rubber gasket are
- It will initially be tight at low bolt forces
- It seems to be less sensitive to varying tightening
- It has a self-sealing function, which provides a matching sealing pressure
- It is robust against displacements between flanges
